Reduction of Oxalate Levels in Tomato Fruit and Consequent Metabolic Remodeling Following Overexpression of a Fungal Oxalate Decarboxylase  

Abstract

The plant metabolite oxalic acid is increasingly recognized as a food toxin with negative effects on human nutrition. Decarboxylative degradation of oxalic acid is catalyzed, in a substrate-specific reaction, by oxalate decarboxylase (OXDC), forming formic acid and carbon dioxide. Attempts to date to reduce oxalic acid levels and to understand the biological significance of OXDC in crop plants have met with little success. To investigate the role of OXDC and the metabolic consequences of oxalate down-regulation in a heterotrophic, oxalic acid-accumulating fruit, we generated transgenic tomato (Solanum lycopersicum) plants expressing an OXDC (FvOXDC) from the fungus Flammulina velutipes specifically in the fruit. These E8.2-OXDC fruit showed up to a 90% reduction in oxalate content, which correlated with concomitant increases in calcium, iron, and citrate. Expression of OXDC affected neither carbon dioxide assimilation rates nor resulted in any detectable morphological differences in the transgenic plants. Comparative proteomic analysis suggested that metabolic remodeling was associated with the decrease in oxalate content in transgenic fruit. Examination of the E8.2-OXDC fruit proteome revealed that OXDC-responsive proteins involved in metabolism and stress responses represented the most substantially up-and down-regulated categories, respectively, in the transgenic fruit, compared with those of wild-type plants. Collectively, our study provides insights into OXDC-regulated metabolic networks and may provide a widely applicable strategy for enhancing crop nutritional value.

Comparative analysis of phytochemicals and nutrient availability in two contrasting cultivars of sweet potato (Ipomoea batatas L.)

“…Several studies on genetic diversity between closely related genotypes had focused on the similarities as well as the difference in the metabolites owing to genetic factors and/or the expression of transgene (Chakraborty et al, 2013;Gayen, Sarkar, Datta, & Datta, 2013;Harrigan et al, 2007). We also found a significant difference in metabolites between the two closely related but contrasting cultivars grown in identical conditions.…”

An Oxalyl-CoA Synthetase Is Involved in Oxalate Degradation and Aluminum Tolerance

“…More interestingly, oxalate is one of the known antinutritional factors, which has negative health concerns, when we consume crops containing high amount of oxalate, such as tomato, spinach, soybean and grass pea (Lathyrus sativus). Chakraborty et al (2013) found that the fruits of transgenic tomato plants expressing a fungus Flammulina velutipes oxalate decarboxylase under the control of fruit-specific promoter have significant less oxalate, but pronounced more nutrients such as Fe and Ca. Constitutive or seed-specific expression of Flammulina velutipes oxalate decarboxylase has also been demonstrated to be not only helpful for improving seed nutritional quality but also tolerance to the fungal pathogen (Kumar et al, 2016).…”

Ripening of Tomato Fruit and Susceptibility to Botrytis cinerea

“…Changes in the concentrations of OA can cause changes in the levels of citric, malic and ascorbic acids. OA is a strong acid and a powerful Ca 2+ chelator (Chakraborty et al 2013 ). B. cinerea secretes signifi cant amounts of OA when infecting leaves (Van Kan 2006 ).…”